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Solar System

The Solar System was formed from the collapse of a giant molecular cloud about 4.6 billion years ago.

The eight relatively solitary planets have almost circular orbits which lie within a nearly flat disc called the ecliptic plane.

Welcome to our Solar System

The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbits around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun. Out of the many objects that orbit the Sun most of the mass is contained within eight relatively solitary planets. Their orbits are almost circular and lie within a nearly flat disc called the ecliptic plane.

The four smaller inner planets, Mercury, Venus, Earth and Mars are called the terrestrial planets because they are primarily composed of rock and metal. The four outer planets are the gas giants and they are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred separately as "ice giants".

Sizes of planets

Solar System components and regions

The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99.86 percent of the system's known mass and dominates it gravitationally. The Sun's four largest orbiting bodies, the gas giants, account for 99 percent of the remaining mass, with Jupiter and Saturn together comprising more than 90 percent.

Inner and outer Solar System

Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are frequently at significantly greater angles to it. All the planets and most other objects orbit the Sun in the same direction that the Sun is rotating (clockwise, as viewed from above the Sun's South Pole). There are exceptions, such as Halley's Comet.

Outer Solar System

The overall structure of the charted regions of the Solar System consists of the Sun, four relatively small inner planets surrounded by a belt of rocky asteroids, and four gas giants surrounded by the Kuiper belt of icy objects. Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the asteroid belt. The outer Solar System is beyond the asteroids, including the four gas giants. Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune.

Above; the movement of Solar Planets as seen from the South Pole of the Sun.

Due to the vast distances involved, typical representations of the Solar System show orbits the same distance apart. In reality, with a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between it and the previous orbit. For example, Venus is approximately 0.33 astronomical units (AU) farther out from the Sun than Mercury, while Saturn is 4.3 AU out from Jupiter, and Neptune lays 10.5 AU out from Uranus.